This allows device drivers to enable MSI (Message Signaled
Interrupts). Message Signaled Interrupts enable a device to
generate an interrupt using an inbound Memory Write on its
PCI bus instead of asserting a device IRQ pin.

Use of PCI MSI interrupts can be disabled at kernel boot time
by using the 'pci=nomsi' option. This disables MSI for the
entire system.

If you don't know what to do here, say Y.

source code:

arch/powerpc/platforms/pasemi/msi.c